feat(daemon): adopt mimalloc-pprof and prove heap, on-CPU, and off-CPU profiling - #1365
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📝 WalkthroughWalkthroughThe workspace adds CPU profiling integration tests and replaces the daemon allocator with ChangesProfiling support
Estimated code review effort: 3 (Moderate) | ~25 minutes Merge Risk: 🟠 High · up to This change adds runtime heap profiling and a heap-dump endpoint, but the endpoint can currently be reached by unauthorized clients and repeatedly trigger profiling work, creating a concrete security and availability risk. Profiling also misses early startup allocations and repeated dumps overwrite previous files, limiting its diagnostic value. Merge should wait until access is restricted and the dump behavior is corrected. Sequence Diagram(s)sequenceDiagram
participant DaemonStartup
participant HeapDumpRoute
participant heap_profile
participant mimalloc_pprof
DaemonStartup->>heap_profile: start_from_env()
heap_profile->>mimalloc_pprof: start sampling
HeapDumpRoute->>heap_profile: dump(None)
heap_profile->>mimalloc_pprof: write pprof snapshot
mimalloc_pprof-->>heap_profile: return snapshot path and sample count
heap_profile-->>HeapDumpRoute: return HeapDumpResponse
🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
✨ Finishing Touches📝 Generate docstrings
🧪 Generate unit tests (beta)
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Inline comments:
In `@crates/fbuild-daemon/src/handlers/health.rs`:
- Around line 84-88: Add authorization or a loopback-peer check to the heap_dump
handler before invoking heap_profile::start or generating a snapshot; reject
unauthorized or non-loopback requests using the daemon’s existing access-control
response behavior, while preserving the current authorized request flow.
In `@crates/fbuild-daemon/src/heap_profile.rs`:
- Around line 129-132: Update the default filename construction in the heap dump
path around NormalizedPath::new so repeated dumps from the same daemon receive
distinct names instead of reusing heap-{pid}.pb. Add a collision-safe sequence
or unique suffix while preserving the existing directory and .pb extension.
In `@crates/fbuild-daemon/src/main.rs`:
- Around line 106-115: Move the fbuild_daemon::heap_profile::start_from_env call
to the beginning of main, before argument parsing and daemon setup, storing its
returned rate. After tracing is initialized, log the stored rate with the
existing heap-profiling message, preserving the conditional logging behavior.
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Fix all unresolved CodeRabbit comments on this PR:
- Push a commit to this branch (recommended)
- Create a new PR with the fixes
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📒 Files selected for processing (10)
Cargo.tomlcrates/fbuild-core/Cargo.tomlcrates/fbuild-core/tests/cpu_profiling.rscrates/fbuild-daemon/Cargo.tomlcrates/fbuild-daemon/src/handlers/health.rscrates/fbuild-daemon/src/heap_profile.rscrates/fbuild-daemon/src/lib.rscrates/fbuild-daemon/src/main.rscrates/fbuild-daemon/src/models.rscrates/fbuild-daemon/tests/profiling.rs
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Cross-platform result from the first CI run, which is the part of #1361 I could not answer locally:
All three profiling tests pass on every platform, including the live on-CPU capture. That was the assertion I most expected to bounce: upstream's own Worth knowing why it works without privileges, since that is what usually breaks this class of test in containers: Linux uses a reserved realtime signal to collect the sibling's The only red was |
…U profiling Closes #1361. Motivated by #1360, where `fbuild-daemon` grew to ~3.9 GB resident while idle and then failed its own health check — and the only tool that could have said *what* was holding the memory was not compiled into the binary. ## The allocator `fbuild-daemon` swaps `mimalloc` for `mimalloc-pprof`: the same mimalloc it already used, with a sampled heap profiler attached. Not feature-gated, on purpose. A profiler compiled out of the shipped binary is never present on the machine where a slow leak reproduces — #1360 was found on someone's real Windows box, twice in one session, and is still not minimally reproducible. The sampler is dormant until started, so the steady-state cost is the allocator swap alone. Note the issue's premise needed correcting: it proposed routing through zccache's `heap_profile` feature, but the pinned zccache (1.13.1, `8cf6dd0`) has no such feature and no `mimalloc-pprof` — those exist only on zccache main. `mimalloc-pprof` is a crates.io crate and zccache's module is a plain re-export, so depending on it directly gets the identical allocator with no zccache repin, which would have dragged `running-process` along with it. ## Two ways in, because leaks are found at two different times - `FBUILD_HEAP_PROFILE=1` (or a byte rate) starts sampling before any heavy init. Startup and static-init allocations are only visible this way. - `POST /api/daemon/heap-dump` works on a daemon that is *already* wedged. This is the half #1360 actually needed: restarting the daemon destroys the leak, so a restart-only profiler cannot answer the question it exists for. When profiling was not already on, the response says so rather than letting a thin profile read as "nothing is leaking". Dumps are pprof `profile.proto`, written under the dev/prod-isolated root via `fbuild_paths` rather than the daemon's CWD. ## Tests — all three modes, not just the wiring - `fbuild-daemon/tests/profiling.rs` — heap. Its `#[global_allocator]` is not incidental: an integration test is its own final executable, so it is the downstream linkage contract the daemon relies on. - `fbuild-core/tests/cpu_profiling.rs` — on-CPU (sampled stacks over a busy thread, then symbolized through `ModuleResolver`) and off-CPU (the async pipeline, asserting it ranks a task that waits 9s above one that burns 500x more CPU — that inversion is the whole point of an off-CPU profile). Two findings worth recording, both of which cost a debugging cycle: - The CPU tests live in `fbuild-core`, not next to the heap test, for a linker reason: `running-process-probe` pulls crash-handler 0.7 while the pinned zccache pulls 0.6.3, and both export the same unmangled C symbols (`ehsetjmp`, `handle_invalid_parameter`, ...). Any binary linking both fails with duplicate symbols. `fbuild-core` is the deepest crate that does not depend on zccache. - The heap test retains 2048 4 KiB blocks rather than one 4 MiB `Vec`. A single large allocation can take mimalloc's large-object path, which does not always pass the sampling hook — that version passed or failed depending on arena state, identically for the same binary run twice. Many small live objects is also the shape a real leak has. `running-process-probe-daemon` needs rusqlite 0.32 while the workspace pinned 0.31, and `links = "sqlite3"` permits only one. Bumped the workspace pin; fbuild-packages (249), fbuild-toolchain (144), fbuild-library, and fbuild-packages-fetch all pass on it. Verified: workspace clippy `-D warnings` clean, fmt clean, both profiling suites stable across repeated runs. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
A full local `dylint --all` sweep on Windows caught four real violations in `heap_profile.rs` that CI would have rejected — worth recording because none were obvious from reading the code: - `default_dump_dir` and `dump` returned `PathBuf` (`ban_std_pathbuf`). Both now return `NormalizedPath`, which is what the workspace uses for a path that crosses an API boundary. - `std::fs::create_dir_all` sat on a path reachable from an axum handler (`ban_std_fs_in_async`, #844) — it would have blocked a tokio worker. `dump` is now async and uses `fbuild_core::fs::create_dir_all`; the pprof write itself stays sync, since it is a C call into the allocator rather than a filesystem-bound operation. - The module's own unit test compared paths with `Path::starts_with` (`ban_raw_path_prefix_compare`, #952). It now compares through `normalize_for_key`, so a verbatim prefix or case difference cannot make the assertion lie. Sweep is now clean workspace-wide. The one remaining violation is `fbuild-core/src/platform/windows/fs.rs`, which this branch does not touch and which reproduces on `main` — filed as #1359, since the Dylint job runs ubuntu-only and has never compiled that file. Refs #1361 Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
`RUSTDOCFLAGS="-D warnings" cargo doc` rejected `[`start_from_env`]` and `[`dump`]` with "no item named ... in scope", even though both are `pub` in the same module. The module carried docs in two places at once — an outer `///` on `pub mod heap_profile;` in lib.rs and the file's own `//!` block — and the merge left the inner links resolving against the wrong scope. Dropped the redundant outer doc (the file's `//!` is the real one) and qualified the links with `self::`, which is unambiguous regardless of how the two blocks merge. Verified: `RUSTDOCFLAGS="-D warnings" soldr cargo doc --workspace --no-deps` is clean. Refs #1361 Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
…ile from process start Three CodeRabbit findings on #1365, all correct: - **The endpoint was reachable off-box.** The daemon binds `0.0.0.0`, and `heap-dump` is not a read: it can switch process-wide profiling on and make the daemon serialize its whole heap on demand. From a network that is both a denial-of-service lever and a way to read allocation shapes off someone else's machine. Nothing about a profiling dump needs to cross a network boundary, so non-loopback callers now get a flat 403 rather than a rate limit. - **Default dump names overwrote each other.** `heap-{pid}.pb` meant the second dump destroyed the first — in a workflow whose entire purpose is *comparing* snapshots over time. Names are now `heap-{pid}-{millis}-{seq}.pb`: the PID separates daemons, the stamp orders snapshots and survives a recycled PID after a restart, and the sequence keeps two dumps inside one millisecond apart. Covered by a test that generates 64 back-to-back names and asserts they are all distinct. - **Profiling started too late to mean what its docs claimed.** The call sat after `Args::parse`, containment setup, `BroadcastHub::new`, and tracing init, so allocations from all of those were permanently unattributable — while the module doc said startup allocations were visible. It is now the first statement in `main`, with the rate logged later once tracing exists to log it to. Refs #1361 Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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@coderabbitai — all three addressed, rebased onto main. Loopback-only heap-dump (Major) — correct and the one that mattered most. The daemon does bind Unique dump names (Major) — also correct, and worse than it reads: the whole point of these snapshots is comparing them over time, so Start before daemon init (Major) — you caught an inconsistency between the code and its own documentation. The module doc claimed startup allocations were visible, but the call sat after Previous run was green on all 92 checks including |
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Closes #1361. Motivated by #1360, where
fbuild-daemongrew to ~3.9 GB resident while idle and then failed its own health check — and the only tool that could have said what was holding the memory was not compiled into the binary.One correction to the issue's premise
The issue (and #1360) proposed routing through zccache's
heap_profilefeature. That feature does not exist at the revision fbuild pins: zccache 1.13.1 (8cf6dd0) has plainmimallocand nomimalloc-pprofat all.heap_profileexists only on zccachemain(1.13.6), which also movesrunning-process— and the rootCargo.tomlrequires those two to be repinned in lockstep or the unmangledrp_*_publicC symbols get linked twice.mimalloc-pprofis a crates.io crate and zccache'sheap_profilemodule is a plain re-export of it, so depending on it directly gets the identical allocator with no repin. That is what this PR does.The allocator
fbuild-daemonswapsmimallocformimalloc-pprof— the same mimalloc, with a sampled heap profiler attached. Not feature-gated, on purpose. A profiler compiled out of the shipped binary is never present on the machine where a slow leak reproduces; #1360 was found on a real Windows box, twice in one session, and is still not minimally reproducible. The sampler is dormant until started, so steady-state cost is the allocator swap alone.Two ways in, because leaks are found at two different times
FBUILD_HEAP_PROFILE=1(or a byte rate) starts sampling before any heavy init. Startup and static-init allocations are only visible this way.POST /api/daemon/heap-dumpworks on a daemon that is already wedged. This is the half fbuild-daemon grows to ~3.9GB while idle then fails health check; heap-profile entry points not wired #1360 actually needed: restarting the daemon destroys the leak, so a restart-only profiler cannot answer the question it exists for. When profiling was not already on, the response says so explicitly rather than letting a thin profile read as "nothing is leaking".Dumps are pprof
profile.proto, written under the dev/prod-isolated root viafbuild_pathsrather than the daemon's CWD.Tests — all three modes, not just the wiring
Per the goal, each mode is demonstrated producing an actual profile:
fbuild-daemon/tests/profiling.rsdump()writes a real file from a running processfbuild-core/tests/cpu_profiling.rsModuleResolverattributes the framesfbuild-core/tests/cpu_profiling.rsThe heap test's
#[global_allocator]is not incidental: an integration test is its own final executable, so it is the downstream linkage contract the daemon relies on.Three findings worth recording
Each cost a debugging cycle and is commented in place:
The CPU tests live in
fbuild-core, not beside the heap test.running-process-probepulls crash-handler 0.7 while the pinned zccache pulls 0.6.3, and both export the same unmangled C symbols (ehsetjmp,handle_invalid_parameter, …). Any binary linking both fails with duplicate symbols.fbuild-coreis the deepest crate that does not depend on zccache.The heap test retains 2048 × 4 KiB blocks, not one 4 MiB
Vec. A single large allocation can take mimalloc's large-object path, which does not always pass the sampling hook — the same binary passed or failed run to run depending on arena state. Many small live objects is also the shape a real leak has.running-process-probe-daemonneeds rusqlite 0.32 while the workspace pinned 0.31, andlinks = "sqlite3"permits only one. Workspace pin bumped; fbuild-packages (249 tests), fbuild-toolchain (144), fbuild-library, and fbuild-packages-fetch all pass on it.Verified locally
clippy -D warningsclean;fmtclean.dylint --allsweep over the workspace on Windows: clean. That sweep caught four violations in the new module before CI could (ban_std_pathbuf×2,ban_std_fs_in_async,ban_raw_path_prefix_compare), all fixed in the second commit.Not in scope
Symbolized function names.
ModuleResolveris the honest floor: it attributes each address to its owning module plus an ASLR-independent offset and names unresolved framesmodule+0xoffsetrather than inventing a name. Getting DWARF/PDB function names depends on[profile.release]'s debug-info settings, not on the profiler — that belongs in its own change, and the test says so rather than asserting on it.Live tokio-console off-CPU capture. The off-CPU pipeline is proven here through
CustomAdapter. A liveTokioAdaptercapture needs console-subscriber wiring in the daemon, which #1360 correctly calls out as a separate change.🤖 Generated with Claude Code
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